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Narendra Modi personally campaigned in the absence of a chief ministerial candidate from his party

The ruling Bharatiya Janata Party's (BJP) decisive win in elections in India's politically crucial state of Uttar Pradesh - it sends 80 MPs to the lower house of parliament, has produced nine prime ministers, and is located next door to the capital, Delhi - is clearly being seen as a referendum on Prime Minister Narendra Modi.

Mr Modi was the face of the campaign in the absence of any clear chief ministerial candidates.

Mixing rhetoric with promises of development, he campaigned hard against what looked like formidable opposition - a coalition of the ruling regional Samajwadi Party (SP) and the Congress, headed by the young satrap Akhilesh Yadav, and the powerful Bahujan Samaj Party, (BSP) led by Dalit leader Mayawati.

So what does this victory mean for his party?

For one, the balance of power in India has now decisively swung in favour of the BJP, and reinforces the party's position as the central pole in India's politics.

The win in Uttar Pradesh - and in the Himalayan state of Uttarakhand - means the BJP now rules more than a dozen of India's 29 state legislatures.

Also, the party appears to have successfully forged a coalition of upper, middle-ranking and lower castes to be able to manipulate the social arithmetic of Indian elections. It has also avoided being seen as doling out reckless patronage to a caste or group - the bane of Mr Yadav's defeated party in Uttar Pradesh.

"He has managed to go beyond the caste arithmetic. On the ground, the BJP is not perceived as a casteist party," Bhanu Joshi, of the Centre of Policy Research, a Delhi-based think tank, told me.

Second, Mr Modi's party appears to have famously survived the jitters over his controversial currency ban, which inconvenienced many people and hurt the poor and small businesses.

Political scientist Milan Vaishnav believes the vote actually "represents a referendum on demonetisation".

"Whether voters were bothered by the implementation of the policy or not, they clearly have decided that the PM is a man of action. As the old saying goes, "you can't beat something with nothing", he told me.

Thirdly, midway through his first term, Mr Modi becomes the front-runner in the 2019 general elections for a second term in power.

This despite what critics say is a lukewarm economic record - the jury is out on whether he's an economic reformer or a believer in big state - and rising social tensions.

One reason is the state of opposition. The main opposition Congress party - despite its apparent win in Punjab - remains in a limbo, run by the dynastic Gandhi family, which holds the party together but is unable to win votes. "No state in India will now vote for a Gandhi," says political analyst Shekhar Gupta.

The defeats in Punjab and Goa are also a big setback for the national ambitions of the promising anti-corruption Aam Aadmi Party, which holds power in its Delhi borough.

Fourthly, the win will mean a huge boost to Mr Modi's party in the upper house of parliament, and help it to push through key laws.

And finally, Mr Modi's connection with the masses remains undiminished.

"Modi is the single most popular politician in India today, bar none. His charisma, perceived personal incorruptibility, and credibility are unmatched right now in Indian politics," says Dr Vaishnav.

"As the opposition keeps railing against him, with very little to show for itself in the way of an affirmative vision, he will continue to gain strength."

That probably is the biggest problem with India's jaded and uninspiring opposition: their inability to take on Mr Modi with a new narrative of hope.

Many like Yogendra Yadav, founder of the Swaraj India party, believe that jolted by the defeat in Uttar Pradesh, the opposition will be pushed to cobble together a "grand anti-Modi alliance" to take on his party in 2019.

But politics is also about the unforeseen and the unpredictable. Nobody predicted that former prime minister Atal Behari Vajpayee, one of the BJP's most charismatic leaders, would lose the 2004 elections to a subdued Congress party-led coalition.